Field of the Invention
The present disclosure relates to a touch sensor-integrated display device, and more particularly, to a touch sensor-integrated liquid crystal display device which is suitable as a display device driven by a vertical electric field.
Discussion of the Related Art
Various input devices, such as a keyboard, a mouse, a trackball, a joystick, a digitizer, and the like, are used to configure an interface between a user and home appliances or various information communication devices. However, the use of the above input devices requires the user to learn how to use them and involves inconvenience like the space occupied by them. Accordingly, there is a growing demand for input devices which are easy and simple to use and can reduce malfunctions. In response to this demand, a touch sensor was proposed to enable the user to directly touch the screen with he/her finger or a pen to input information.
The touch sensor is simple to use, has less malfunctions, and enables the user to input without using an additional input device. In addition, the touch sensor can be applied to various display devices because it enables the user to operate it quickly and easily through content displayed on the screen.
The touch sensor used for display devices can be classified into add-on type, on-cell type, and integrated type (or in-cell type) according to its structure. In the add-on type, a display device and a touch panel having a touch sensor are separately manufactured, and the touch panel is attached onto an upper substrate of the display device. In the on-cell type, a touch sensor is directly formed on the surface of an upper glass substrate of a display device. In the integrated type, touch sensor elements are integrated into a display device to make the display device thin and improve the durability of the display device.
Among them, the integrated type touch sensor is relatively widely used because it reduces thickness by using common electrodes of the display device as touch electrodes and also improves durability by forming touch elements inside the display device.
A typical display device to which the integrated type touch sensor is applied is a liquid crystal display device. The liquid crystal display device generally comprises a liquid crystal display panel with a thin film transistor array and a color filter array disposed to face each other with a liquid crystal layer interposed between them.
Such liquid crystal display devices are classified into a vertical electric field type and a horizontal electric field type depending on where a common electrode and a pixel electrode are formed with respect to the liquid crystal layer. In the vertical electric field type, the common electrode and the pixel electrode are disposed to face each other with the liquid crystal layer interposed between them and driven to apply a vertical electric field to the liquid crystals, and in the horizontal electric field type, the common electrode and the pixel electrode are arranged at one side of the liquid crystal layer and driven to apply a horizontal electric field to the liquid crystals. The vertical electric field type comprises a TN (Twisted Nematic) mode type and a VA (Vertical Alignment) mode type, the horizontal electric field type comprises an IPS (In Plane Switching) mode type and an FFS (Fringe Field Switching) mode type.
In a related art horizontal electric field type touch sensor-integrated liquid crystal display device, both a common electrode and a pixel electrode are formed on a transparent substrate (i.e., lower transparent substrate) of a thin film transistor array to apply a horizontal electric field to the liquid crystals and drive the liquid crystals, the common electrode is segmented into touch electrodes also serving as common electrodes, and a display operation and a touch operation are performed in a time division manner. Each of the segments of the common electrode may serve either a touch driving electrode or a touch sensing electrode, or may be used as a touch driving and sensing electrode.
An example of the horizontal electric field type touch sensor-integrated liquid crystal display device will be described briefly with reference to FIG. 1.
FIG. 1 is a schematic cross-sectional view for explaining the operating principle of a related art horizontal electric field type touch sensor-integrated liquid crystal display device.
Referring to FIG. 1, a thin film transistor array TFTA includes a pixel electrode Px and a common electrode COM that form a horizontal electric filed on a liquid crystal layer LC by a pixel electrode Px and a common electrode COM formed on another layer. The common electrode COM also functions as a touch sensor, and is segmented into a plurality of touch driving electrodes Tx and a plurality of touch sensing electrodes Rx.
A color filter array CFA is arranged on the thin film transistor array TFTA, with a liquid crystal layer LC interposed between them, and window glass W is arranged on the color filter array CFA.
As shown in FIG. 1, the liquid crystals of the liquid crystal layer LC are driven by an electric field formed between the pixel electrode Px and the common electrode COM, and the capacitance between the touch driving electrodes Tx and the touch sensing electrodes Rx changes by touching the window glass W above the color filter array CFA with a finger F. Therefore, a touch and a touch position can be detected by performing a display operation and a touch operation in a time division manner.
However, the above-described related art horizontal electric field type touch sensor-integrated liquid crystal display device has the problem that a common electrode is formed on a thin film transistor array TFTA and is therefore not applicable to a vertical electric field type touch sensor-integrated liquid crystal display device.
Accordingly, there arises the need for a vertical electric field type touch sensor-integrated liquid crystal display device which is applicable to a vertical electric field type liquid crystal display device.
By the way, segmenting a common electrode of the vertical electric field type liquid crystal display device and using the segments of the common electrode as touch electrodes involves the following problems.
First, when segmenting a common electrode formed on the color filter array CFA and using the segments of the common electrode as common electrodes for the display operation and touch electrodes for the touch operation, a low-resistance metal line needs to be connected to each of the segments (i.e., touch electrodes) of the common electrode in order to supply a common voltage or a touch driving voltage. The metal line connected to each of the segments of the common electrode needs to extend from a display area (active area) to a non-display area (bezel area) outside the display area. Accordingly, any overlap between the metal line and color filters lowers aperture ratio and display quality.
Second, since horizontal electric field type liquid crystal display device is configured in such a way that the segments of the common electrode and metal lines connected to the segments are formed in the thin film transistor array, there was no particular problem with connecting a source driver IC (integrated chip) for the display operation to a touch IC for the touch operation. On the other hand, the vertical electric field type liquid crystal display device is configured in such a way that the segments of the common electrode and metal lines connected to the segments are formed in the color filter array and a source driver IC (integrated chip) for the display operation and a touch IC for the touch operation are formed in the thin film transistor array. As the color filter array and the thin film transistor array are disposed to face each other with the liquid crystal layer interposed between them, it was difficult to connect the metal line formed in the color filter array to the source driver IC and touch IC formed on the thin film transistor array.